1. Field of the Invention
The present invention relates to a cutting apparatus for cutting a workpiece such as a semiconductor wafer with precision.
2. Related Art
FIG. 7 shows a semiconductor wafer cutting apparatus. It comprises a holder means 15 for holding a workpiece to be cut, a cutting means 23 including a rotary blade 24 for cutting the workpiece held by the holder means 15, an alignment means 36 having an imaging means 37 equipped therewith, and other associated parts. As seen from the drawing, a semiconductor wafer W is attached to a holder frame F using a piece of adhesive sheet T, and the wafer-bearing holder frame F is held on the holder means 15. The holder means 15 is driven in the X-axial direction to be just below the alignment means 36, allowing the alignment means 36 to detect a selected street along which the semiconductor wafer W is to be cut, and then, the holder means 15 is further driven in the X-axial direction while the cutting means 23 is lowered, thus allowing the rotary blade 24 to cut the semiconductor wafer W along the selected street.
The alignment means 36 and the cutting means 23 are integrally connected to each other, so that these parts may be moved as a whole in the Y- and Z-axial directions. The alignment means 36 is equipped with the imaging means 37, e.g., comprising a CCD camera. As shown in FIG. 8, the imaging means 37 has an imaging screen 38 in which a hairline 39 is drawn as a reference line in the X-axial direction.
Before cutting the semiconductor wafer along a selected street, it is necessary that the rotary blade 24 be set in alignment with the hairline 39 in the X-axial direction, as shown in FIG. 9. The imaging means 37 is moved in the Y-axial direction to scan an image of the selected street along which the semiconductor wafer W is to be cut, and a required adjustment is made until the selected street is found in alignment with the hairline 39, which means that the rotary blade 24 is put in alignment with the selected street.
After establishing the alignment of the rotary blade 24 with the selected street to be cut, the holder means 15 is driven in the X-axial direction while the cutting means 23 is lowered in the Z-axial direction, thus allowing the rotary blade 24 to cut the semiconductor wafer W along the selected street.
Every time the cutting means 23 is moved by a street-to-street interval in the Y-axial direction, the cutting operation is resumed. Finally the semiconductor wafer W is cut along all streets in the X-axial direction. Then, the wafer-holding table 15 is rotated 90 degrees to repeat the cutting operation of the semiconductor wafer. Thus, the semiconductor wafer W is cut crosswise into squares.
Required precise cutting can be attained provided that the rotary blade 24 is aligned exactly with the hairline 39 in terms of their Y-coordinate. Such alignment, however, cannot be attained, for instance, if a new rotary blade is used in place of the old one; rotary blades cannot be exactly the same, but they are somewhat different from each other to the extent of causing misalignment between the new rotary blade and the hairline in terms of their Y-coordinate.
As seen from FIGS. 10(A) and 10(B), the rotary blade 24 is press-fitted on a rotary spindle 50, and then a screw nut 51 is applied to a threaded-end 52 of the rotary spindle 50 to tighten the rotary blade 24 with the screw nut 51, sandwiching the rotary blade 24 between a mount flange 53 and the screw nut 51. The position of the rotary blade 24 on the spindle 50 will minutely vary according to a degree of fastening or tightening with the screw nut 51 and the like, and it is very difficult to fasten a new rotary blade 24 as tightly as in another or old one, in case of, e.g., changing the rotary blade. Therefore, the new rotary blade 24 would usually be spaced apart more or less from the hairline 39.
Conventionally, in replacing the rotary blade with a new one, a dummy wafer is held by the holder means 15, and then the new rotary blade is used to cut a straight groove 54 on the dummy wafer. The imaging means 37 is used to scan an image of the straight groove 54. If the image of the straight groove 54 is not found in alignment with the hairline 39 (see FIG. 11), an adjusting screw is rotated until the image of the straight groove 54 has been put in alignment with the hairline 39 (see FIG. 12). This is tedious, time-consuming work.
Assuming that the rotary blade 24 happens to be broken while cutting a semiconductor wafer, the broken rotary blade 24 must be removed from the rotary spindle 50 to be replaced with a new one, following a series of actions beginning with the changing of the broken rotary blade for a dummy wafer and ending with the aligning of the straight groove made on the dummy wafer with the hairline.
Subsequent to the alignment effected on the dummy wafer relative to the hairline 39, the dummy wafer must be removed from the holder means 15 to put the unfinished semiconductor wafer in place of the dummy wafer, and again an image of the unfinished cut along the selected street is scanned for alignment with the new rotary blade before resuming the cutting of the semiconductor wafer. This is a significant cause of lowering the workability and productivity.
One object of the present invention is to enable the changing of rotary blades in a cutting machine without requiring such tedious, time-consuming work as described above.
To attain this object, the present invention provides a cutting apparatus comprising at least a holder means for holding a workpiece to be cut and a cutting means including a rotary blade for cutting the workpiece held by the holder means, where the holder means and the cutting means are adapted to be driven relative to each other in a cutting direction, an indexing direction and a blade-thrusting direction, which apparatus further comprises a marking member positioned at such a place that the rotary blade can make a mark of cutting position (alignment marks) in an indexing direction on the marking member in order to align the rotary blade with a cutting line on the workpiece.
The marking member may be of an abrasion-resistant material.
The abrasion-resistant material may be a hard urethane.
The cutting apparatus may further comprise an alignment means having an imaging means for scanning a cutting area of the workpiece held on the holder means in order to align the cutting area and the rotary blade with each other with respect to the indexing direction, the imaging means having an imaging screen with a hairline drawn as a reference line for the alignment on the screen, wherein the mark of cutting position made on the marking member is scanned by the imaging means and imaged on the screen, while the mark of cutting position is aligned with the hairline on the screen, whereby the alignment of the cutting area with the blade is attained.
Thanks to the marking member the quick and easy alignment of the rotary blade relative to the hairline is permitted without using a dummy wafer. If the marking member is made of an abrasion-resistant material, marks made on the marking member become invisible in a while, thus permitting the marking member to be used repeatedly.
Further, even when a rotary blade is broken during the cutting operation, the broken blade can be readily changed without putting an operator to such a bother as in the conventional cutting machine.